Gas heat exchanger unit

ABSTRACT

Compact dedusting heat exchanger, characterized in that the heat exchange unit consists of a superimposing of a certain number of metal lattices, the assembly having the form of a metal conveyor in a closed loop moving continuously, passing through a hot gas compartment then a cold gas compartment.

United States Patent Carrasse et al.

[ Nov. 11, 1975 [5 GAS HEAT EXCHANGER UNIT 2,898,091 8/1959 Verbeek165/10 3,126,945 3/1964 Kuhner 1 165/6 [751 Inventors carrasse Antony;Jacques 3,651,862 3/1972 Ballinger 165/6 Gerard, Saint-Ouen; PierrePounhet, ifi Theme Marti! Paris FOREIGN PATENTS OR APPLICATIONS I rance789,970 1/1958 United Kingdom 165/6 [73] Ass1gnee: Societe Generale deConstructions 919,596 2/1963 United Kingdom 165/6 Electriques etMecaniques 1,124,528 3/1962 Germany 165/6 (ALSTHOM), France 443,64612/1948 Italy 165/6 [22] Filed: Nov. 2, 1972 Primarv ExaminerA1bert W.Davis Jr. 21 A l. N 1 1 PP O 303080 Attorney, Agent, or Firm-Craig &Antonelll [30] Foreign Application Priority Data Nov. 2, 1971 France71.39313 5 ABSTRACT [52] US. Cl. 165/5; 165/6; 165/9; Compact dedustingheat exchanger, characterized in 165/ 10; /383; 15/404; 15/415 that theheat exchange unit consists of a superimpos- [51] Int. Cl. FZSd 19/ 00ing of a Certain number of metal lattices the assembly [58] Fleld ofSearch 165/6, 5, 10, 9, having the form of a metal Conveyor i a closed lmoving continuously, passing through a hot gas com- [56] References cuedpartment then a cold gas compartment.

UNITED STATES PATENTS 1,697,591 1/1929 Dowd, Jr. /6 11 Claims, 8 DrawingFigures I K 1 1 1 t l 1 x 1 9 g 1 g 1 1 i I 6 1 9 7 I 1 a I I Sheet 1of4 US. Patent Nov. 11, 1975 1 T1 IL.

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Sheet 2 of4 3,918,516

US. Patent Nov. 11, 1975 Sheet3of4 3,918,516

US. Patent Nov. 11, 1975 FIGS US. Patent --Nov. 11, 1975 Sheet4 0f43,918,516

FIG.6

GAS HEAT EXCHANGER UNIT The object of the present invention is a compactgas heat exchanger and heater unit in which the very structure of theheat exchange unit enables the dedusting of the gases passing across it,for example, hot smoke coming from a power station boiler. Moreover, thecleaning of the heat exchange unit itself is easy and may be effectedcontinuously. Furthermore, the invention also allows the removal ofsulphurous products from smoke.

More particularly but not exclusively, the object of the invention is anair heat exchanger and heater unit for a boiler in a large powerstation.

There exist, at present, heat exchangers ensuring that function, forexample, LJUNGSTROM and R- THEMUHLE rotating heat exchangers, but theirdimensions limit the use thereof; furthermore, heat exchange takes placeover a great length, for example two meters, as does the depositing ofsoot, this making cleaning of the metal sheets difficult; moreover, themobile unit is subjected to numerous differential expansions which leadto difficulties in manufacturing and operating. Likewise, a part of themetal sheets is constantly damp and subjected to the combined action ofthe soot deposits and of the condensing of sulphuric acid coming fromthe water vapour and the 50;, of the smoke. Despite the use, in the lowand cold part of the heat exchanger, of enameled metal sheets, or metalsheets made from special steel which resist acid corrosion, thereplacing of the heat exchange units, or at least the cleaning thereof,makes frequent and relatively long stoppages of the installationcompulsory. Another disadvantage is that it is not possible to inspectthe heat exchanger, for example, to clean the plates or change themwithout stopping the boiler.

The aim of the present invention is to overcome these disadvantages and,more particularly, it enables good dedusting of smoke, maintenance,inspection or replacement of wear elements without stopping the boiler,detection in various zones of soot deposits, on the one hand, and dampsulphuric acid deposits on the other hand, thus avoiding the forming ofsmoky charcoal.

Another advantage resides in the fact that the wear elements areindependent from one another and that each of them is subjected, at agiven instant and as a whole, to the same temperature conditions andalso to the, same dampness conditions, contrary to the case of aforesaidrotating exchangers, having a constantly dry zone and a constantly dampzone. Moreover, in these aforesaid exchangers, the heat exchange takesplace in the volume, as does the depositing of soot; in the case of theinvention, the heat exchange takes place in a volume, which is,moreover, much shorter, whereas the depositing of soot or dust iseffected mainly at the surface, thus making the cleaning of the heatexchange unit easier.

The gas heat exchanger and heater unit according to the inventioncomprises at least one heat exchange unit in the form of a closed loopmetal conveyor moving continuously or in jerks crossing successively, intwo crossed passes and against the gas current, each of the hot gas andcold gas compartments, and is characterized in that the said metalconveyor consists of a set of independent elementary sieves eachconstituted by the superimposing of a great number of layers of metallattices, in that the hot gas and cold gas compartments are separated byan intermediate compartment in which are installed cleaning anddust-removing devices. Two compartments, the one placed at the upperpart of the heat exchanger, the other at the lower part, both separatedfrom the smoke and air compartments, contain at least a part of themechanical drive and rolling means of the conveyor, in that thesecompartments are accessible during the operation of the installation,and in that, in the compartments, the sieves may be inspected anddismantled separately.

The number of layers of metal lattices may be very great, thisincreasing the heat exchange surface by the crossing of the conveyor andenables the number of passes of the conveyor in each compartment to belimited. The separation into independent solid elements connected to oneanother in the form of an articulated conveyor enables, despite thegreat number of layers of metal lattices, the driving of the unit bysimple means and avoiding any mechanical or thermic stresses which mightotherwise result from the accumulation in relatively thick layers ofmoving metallic masses subjected to the action of heat.

According to a particular embodiment of the present invention, the saidelementary sieves are each constituted by solid frames enclosing thesaid superimposing of metal lattices, the said conveyor beingconstituted by a succession of these said frames, which are each fixedlaterally to two drive chains, each frame being fixed to each chain atthe two ends of a same chain link, thus enabling rapid dismantling ofthe frames for repairs, replacements or more thorough cleaning.

According to a particular form of that embodiment, and to makefluid-tight sealing between the various compartments easier, the drivelinks are fast with the frames in their lateral faces, the chain linksbeing articulated between two successive frames on these same faces.

In the case of independent chains, an upper shaft provided with two cogwheels enables simultaneously the supporting of the conveyor and thedriving thereof, by means of chains, an identical device in the lowerpart simplyguided vertically enables the mobile unit to be sent back andsubjected to tightening, taking into account the expansion of theconveyor.

In the case of integrated links, an upper drum and a lower drum onlyfulfill the functions of a support and a bearing, drive being providedby independent means, for example, cog wheels or lateral worm screwsplaced either in a mechanical compartment, or in the air compartment,and coming into gear in lateral openings of the frames forming links asstated above.

Preferably, the first and second layers of metal lattices of each frameare constituted by a metal lattice having finer meshes than the insidelayers, and, moreover, either a perforated metal sheet whose holes arelarger than the meshes of the inside metal lattices, or a solid gridhaving large meshes, are arranged on each side of the assembly thusformed.

Cleaning and dedusting devices are arranged in the intermediatecompartment; to great advantage, it is possible, for example, to placemeans for sending, with an adjustable speed and direction, one orseveral jets of gas or steam against the face of the metal conveyor onwhich dust is deposited. It has indeed been observed that this methodaffords a greater advantage than sending the jet(s) in the reversedirection to the path of the hot unclean gases; this comes from the verystructure of the metal'conveyor; the first layer of metal lattices beingvery fine, the dust remains on the surface against that first'layer andalso in the holes of the perforated metal sheet placed on the outside,without penetrating deep into the inside layers; moreover, the knowndust precoating effect occurs, improving the filtering qualities of themetal conveyor, and experience shows that by blowing on the dust depositside, a good result is obtained without forasmuch destroying thatfiltering precoating. This action may be combined with brushing and alsowith blowing at low speed in the reverse direction, the aim of thisbeing not so much to clean but by blowing in the reverse direction, toremove dust already knocked away by jets blowing in the normal directionin the direction of the dust deposit.

The direction and the speed of the steam or gas jets against theconveyor, on the dust depositside, evidently depends on the grain sizeof the dust or soot, or their adhering power, on the temperature, etc.

It is also possible, besides blowing in the reverse direction, to removedust already knocked off, to arrange, moreover, high gas or steampressure jets for intermittent deep cleaning, or when, for example, theabove-mentioned precoating becomes too thick. Indeed, a small amount ofdust always penetrates into the deep layers.

According to another particular embodiment of the present invention, thesaid elementary sieves are constituted by a set of elementarytransversal strips each constituted by a stack of metal lattices, thesaid transversal elementary strips being arranged on at least twosuperimposed layers, each layer being constituted by a succession of thesaid elementary strips placed end to end, the elementary strips of thetop layer being staggered in relation to the elementary strips of thebottom layer, each elementary strip of the top layer being fixed alongone of its edges to the top elementary layer placed on that edge. Eachelementary transversal strip of the lower layer is fixed to two drivechains, at a point of two of its opposite sides.

Other characteristics and advantages of the present invention willbecome apparent from the following description with reference to theaccompanying'drawings.

FIG. 1 is an air heat exchanger and heater unit for a boiler accordingto the invention;

FIG. 2 shows diagrammatically a heat exchanger according to theinvention, in which the gases cross the metal conveyor four times;

FIG. 3 gives an example of the assembling of elementary transversalstrips;

FIG. 4 shows diagrammatically an embodiment of the metal conveyor formedby frames installed between two chains; 1 I

FIG.'5 shows an air heat-exchanger and heater unit according to'theinvention, showing the fluid-tight sealing and cleaning devices;

FIGS. 6 and 7 are enlarged views of the intermediate compartment showingthe cleaning devices; and

FIG. 8 is a cross section of a frame enclosing the metal lattices.

The air heater unit in FIG. 1 is composed essentially of a heatexchanger unit 1 in the form of a closed loop conveyor, constituted bythe superimposing of metal lattices; that heat exchanger unit is drivenin a continuous or jerky movement in the direction shown by the arrows,by means of a motor unit 2 and comprises, at

its lower part,'an idle pulley 3 provided with a device which provides aconstant tension of the heat exchanger unit 1, despite variations intemperature. That heat exchanger unit 1 passes through a compartment 4crossed in the direction of the arrows by hot smoke coming from theboiler and a compartment 5, crossed by the air supply of the boiler inthe direction of the ar- I'OWS.

On passing through the heat exchanger unit 1, the hot smoke cools down,heating the heat exchanger unit 1,

and in the compartment 5, the air supply is heated by absorption of thecalories which the heat exchanger unit has received from the hot smoke.

In an intermediate compartment 6, the cleaning of the heat exchangerunit 1 by permanent brushing by means of brushes 7 and 8 takes place.

An opening 9 in the intermediate compartment 6 makes it possible tosample, in the compartment 4 a part of the clean hot smoke which hasalready passed once across the heat exchange unit 1 and to send it backagainst the current into the intermediate compartment through the heatexchanger unit I to remove the soot which has been knocked off by thebrushes 7 and 8. In that heat exchanger and air heater unit, the smokereleased into the atmosphere is clean, for it has been rid of its sooton passing across the heat exchanger unit 1 which hasa meshed structure.That heat exchanger and air heater unit has, moreover, the advantage,compared with the conventional devices mentioned above, such asLJUNGSTROM or ROTI-IEMUI-ILE, of being much more compact and lighter,clue to that meshed structure of the heat exchange unit, which, for asame vol ume, has a much greater heat exchange surface because it ismore finely divided.

Fluid-tight sealing devices, not shown in the figure, are providedbetween the various compartments; these latter do not, moreover, need tobe perfect; indeed, a

certain leakage may be tolerated. Furthermore, the fluid-tight sealingis greater than that of the other types of heat exchangers because ofthe great reduction in the length of the leakage lines. One advantage isthe considerable reduction in the danger of fire subsequent to thepermanent cleaning of the heat exchanger unit. In order to make thededusting more efficient, the first layer in contact with the smoke mayhave finer meshes than those of the following layers. Another advantageof the system in the present invention is its corrosion characteristic,which distributes the corrosion evenly throughout the heat exchangesurface due to the fact that the latter moves.

In the heat exchanger in FIG. 1, the smoke and the air pass twice acrossthe heat exchanger unit, but it is possible either to have two orseveral heat exchanger units in succession, or to adopt the arrangementin FIG. 2, in which four passes are shown by the arrow line 10 for thesmoke and by the arrow line 11 for the air.

The order of magnitude of the moving speed of the metal conveyor 1 is afew tens of centimeters per second and depends on the air flow.

Another advantage of the present invention is that it ispossible toinstall, in the intermediate compartment 6 and/or in the hot gascompartment, a desulphurization system. The situation of thecondensation zone makes it possible to proceed with the neutralizing oithe sulphurous compounds by injecting a neutralizing gas or solid. Themovement of the heat exchanger unit, which passes from a cold zone to ahot zone makes drying by evaporation of that mass possible. Thesulphurous products, in the dry form, may then be recuperated in thededusting zone which follows the hot zone.

FIG. 3 gives an example of a structural arrangement of the metalconveyor 1; it is made of elementary strips 12; each one is constitutedby a stack of metal lattices. These elementary strips 12 are arranged intwo superimposedlayers. Each element is fixed to a bottom element byspot welding 13. The figure shows that the elements of the top layer arestaggered in relation to the elements of the bottom layer. The conveyorthus formed is fixed by the bottom layer, at 14, to two parallel drivechains. This fragmentary structure of the metal conveyor and the way inwhich the elements 12 are assembled and fixed to the chains enables theconveyor to follow the curves of the loop closed, for example, at theidle pulley 3 and at the drive pulley 2, without damaging the metallattices.

This fragmentary arrangement also enables the rapid dismantling of theelements, either to replace them, or to clean them more thoroughly.

Preferably, in heat exchangers for a high air flow, the metal conveyor 1is constituted by a succession of rigid frames (FIG. 4) which enclose astack of metal lattices 16. Each frame 15 is fixed to two drive chains17 and 18 at two points 19, 20 and 21, 22, of two of the sides of theframe, at the ends of two chain links 23. Fluid-tight sealing isprovided at 24 between each consecutive frame.

FIG. 5 shows a heat exchanger similar to that in FIG. 2, in whichfluid-tight sealing means and cleaning and blowing means in theintermediate compartment 6 have been shown. The fluid-tight sealingmeans are constituted by mobile boxes 25, suspended by counterweights 26and articulated by parallelograms 27 enabling movements, limited byflexible suspension means 28. These boxes comprise sealing rings 29forming break joints, for example, for the flexible metal sheets. Thereare, moreover, flexible fluid-tight partitions 30.

In the case of a drive by independent chains, these horizontalfluid-tight sealing means are completed by vertical lines of sealspressing against the lateral edges of the frames preventing air frompassing in the chain pass funnels.

In the case of a drive by links fast with the frames, horizontal meansare also installed on the lateral edges of the frames forming acontinuous barrage at the level of the crossing of the conveyor from onecompartment to the next.

Cleaning and dedusting devices which have been shown on an enlargedscale in FIGS. 6 and 7 have also been shown in that figure. In thesefigures, cleaning is effected by blow nozzles 31 which may be directed,blowing on the face of the conveyor 1 on which the dust has beendeposited; a brush 32 may also be provided. The dust knocked off is thenremoved, for example by sampling the air across the conveyor over allthe face of the compartment. (see the arrows 33, FIG. 6).

Deep periodic cleaning may also be effected by means of a blow nozzlesystem 34 for steam or compressed air at a high pressure, lasting ashort while.

FIG. 8 shows a cross section of a frame of the metal conveyor comprisingthe actual metal frame 35, a cover 36, two perforated metal sheets orelse two largemesh grids 37, as will be seen in an enlarged illustrationin FIG. 7, two metal lattices or fine-mesh sieves 38 and lastly, twolayers of metal lattices or medium-mesh sieves 39.

Another advantage of the present invention is that the conveyor may beinspected in a compartment 40 (FIG. 5) without stopping the device, andthat it is even possible, by then stopping the conveyor, but withoutstopping the boiler, that is, while continuing to supply the boiler withair, in the direction of the arrows 41, and while providing the removalof the hot gas in the .direction of the arrows 42, to dismantle theframes of the conveyor for cleaning, repair or evenchanging. Thepossibility of dealing with the heat exchanger without stopping theboiler and without forasmuch there being any danger of damaging theheater exchanger unitpermanently, on account of its independent elementstructure, constitutes a great advantage of the invention compared withknown devices having compact heat exchanger units with large dimensions.

A great advantage of the invention is that there is never a combinationof soot and liquid sulphuric acid. Indeed, at the input of the hot gasin the compartment 4, the conveyor is at high temperature, and there isno condensation of sulphuric acid, but only a deposit of soot; on theother hand, when the conveyor arrives at 43 in the compartment 4 afterhaving left the fresh air compartment 5, that cold heat exchanger unitbelow dew point meets the gas which is already partly cooled and chargedwith S0 there is then a condensation of sulphuric acid, but on a cleanconveyor, for it has been cleaned in the intermediate compartment 6.Then the conveyor continues its travel and is heated on rising from thepoint 43 to the point 44 and when it reaches 45, the temperature ishigher than the dew point of sulphuric acid. Moreover, a neutralizingsubstance which will form a solid compound which at first is wet at 43and 44, becoming completely dry during its transfer through 45 andbeyond so that it may be removed in a dry form in the same way as thesoot in the intermediate compartment 6, may be injected at the point 43.

It must be understood that certain technological elements could besubstituted for others described above which fulfill the same function,without forasmuch departing from the general idea of the invention, notgoing beyond the scope thereof.

What is claimed is:

l. A gas heat exchanger unit comprising, a hot gas compartment and acold gas compartment, at least one heat exchanger unit in the form of aclosed loop metal band mounted for movement through both of said hot andcold gas compartments along first and second paths transverse to the gasflow therethrough, said metal band being formed by a plurality ofindependent elementary sieves interconnected to form the band andconstituted by a plurality of layers of metal lattices, and intermediatecompartment disposed between said hot and cold gas compartmentstraversed by said metal band, cleaning means disposed in saidintermediate compartment for removing dust from the band passingtherethrough, and means for driving said band along a closed loop path,wherein said cleaning means includes means for intermittently directingjets of gas at high speed onto the band against the opposite surfacefrom the dust deposit.

2. A gas heat exchanger unit as defined in claim 1, further includingfirst and second outer compartments disposed adjacent said hot and coldgas compartments on the sides thereof opposite said intermediatecompartment in which said means for driving said bank are disposed, atleast one of said first and second outer compartments being providedwith means for permitting inspection of said band.

3. A gas heat exchanger unit as defined in claim 1 wherein saidelementary sieves are each formed by solid frames enclosing-saidplurality of layers of metal lattices, said driving means including apair of drive chains to which each frame of the elementary sieves isfastened in succession to form the metal band.

4. A gas heat exchanger unit as defined in claim 3 wherein said drivingmeans further includes first and second sets of sprocket wheels engagingsaid pair of drive chains for driving said band, the links of said drivechains being articulated between successive frames of said sieves.

5. A gas heat exchanger unit as defined in claim 3 wherein the outerlayers of metal lattices of each sieve have a finer mesh than the innerlayers, and further including a metal sheet having holes larger than theholes in said metal lattices disposed outside of said lattices onrespective sides of the frame of each sieve.

6. A gas heat exchanger unit as defined in claim 1 wherein said cleaningmeans further includes means for directing at least one jet of gasagainst the face of said metal band in an adjustably variable direction.

7. A gas heat exchanger unit as defined in claim 1 wherein said cleaningmeans further includes brush means for mechanically brushing the surfaceof said metal band.

8. A gas heat exchanger unit as defined in claim 7 wherein said cleaningmeans further includes means for directing at least one jet of gasagainst the face of said metal band in an adjustably variable direction.

9. A gas heat exchanger unit as defined in claim 1 wherein saidelementary sieves are formed by a set of transverse elementary stripseach constituted by a plurality of metal lattices arranged in at leasttwo superimposed layers, each layer being constituted by a succession ofsaid elementary strips placed end-to-end, the elementary strips of thetop layer being staggered in relation to the elementary strips of thebottom layer, each elementary strip of the upper layer being fixed alongone of its edges to the bottom elementary layer situated under thatedge.

10. A gas heat exchanger unit as defined in claim 9 wherein eachelementary strip of the bottom layer of each sieve is fixed to a pair ofdrive chains forming part of said drive means.

11. A gas heat exchanger unit as defined in claim 1 wherein saidintermediate compartment includes movable boxes suspended flexiblysurrounding the metal band and sealing rings for sealing the entranceand exit openings for the band in said boxes.

1. A gas heat exchanger unit comprising, a hot gas compartment and acold gas compartment, at least one heat exchanger unit in the form of aclosed loop metal band mounted for movement through both of said hot andcold gas compartments along first and second paths transverse to the gasflow therethrough, said metal band being formed by a plurality ofindependent elementary sieves interconnected to form the band andconstituted by a plurality of layers of metal lattices, and intermediatecompartment disposed between said hot and cold gas compartmentstraversed by said metal band, cleaning means disposed in saidintermediate compartment for removing dust from the band passingtherethrough, and means for driving said band along a closed loop path,wherein said cleaning means includes means for intermittently directingjets of gas at high speed onto the band against the opposite surfacefrom the dust deposit.
 2. A gas heat exchanger unit as defined in claim1, further including first and second outer compartments disposedadjacent said hot and cold gas compartments on the sides thereofopposite said intermediate compartment in which said means for drivingsaid bank are disposed, at least one of said first and second outercompartments being provided with means for permitting inspection of saidband.
 3. A gas heat exchanger unit as defined in claim 1 wherein saidelementary sieves are each formed by solid frames enclosing saidplurality of layers of metal lattices, said driving means including apair of drive chains to which each frame of the elementary sieves isfastened in succession to form the metal band.
 4. A gas heat exchangerunit as defined in claim 3 wherein said driving means further includesfirst and second sets of sprocket wheels engaging said pair of drivechains for driving said band, the links of said drive chains beingarticulated between successive frames of said sieves.
 5. A gas heatexchanger unit as defined in claim 3 wherein the outer layers of metallattices of each sieve have a finer mesh than the inner layers, andfurther including a metal sheet having holes larger than the holes insaid metal lattices disposed outside of said lattices on respectivesides of the frame of each sieve.
 6. A gas heat exchanger unit asdefined in claim 1 wherein said cleaning means further includes meansfor directing at least one jet of gas against the face of said metalband in an adjustably variable direction.
 7. A gas heat exchanger unitas defined in claim 1 wherein said cleaning means further includes brushmeans for mechanically brushing the surface of said metal band.
 8. A gasheat exchanger unit as defined in claim 7 wherein said cleaning meansfurther includes means for directing at least one jet of gas against theface of said metal band in an adjustably variable direction.
 9. A gasheat exchanger unit as defined in claim 1 wherein said elementary sievesare formed by a set of transverse elementary strips each constituted bya plurality of metal lattices arranged in at least two superimposedlayers, each layer being constituted by a succession of said elementarystrips placed end-to-end, the elementary strips of the top layer beingstaggered in relation to the elementary strips of the bottom layer, eachelementary strip of the upper layer being fixed along one of its edgesto the bottom elementary layer situated under that edge.
 10. A gas heatexchanger unit as defined in claim 9 wherein each elementary strip ofthe bottom layer of each sieve is fixed to a pair of drive chainsforming part of said drive means.
 11. A gas heat exchanger unit asdefined in claim 1 wherein said intermediate compartment includesmovable boxes suspended flexibly surrounding the metal band and sealingrings for sealing the entrance and exit openings for the band in saidboxes.